U.S. patent application number 14/336669 was filed with the patent office on 2014-11-06 for lithium ion battery.
The applicant listed for this patent is GM Global Technology Operations, LLC. Invention is credited to Timothy J. Fuller, Ion C. Halalay, Stephen J. Harris.
Application Number | 20140329143 14/336669 |
Document ID | / |
Family ID | 44151579 |
Filed Date | 2014-11-06 |
United States Patent
Application |
20140329143 |
Kind Code |
A1 |
Halalay; Ion C. ; et
al. |
November 6, 2014 |
LITHIUM ION BATTERY
Abstract
In a lithium ion battery, one or more chelating agents may be
attached to a microporous polymer separator for placement between a
negative electrode and a positive electrode or to a polymer binder
material used to construct the negative electrode, the positive
electrode, or both. The chelating agents may comprise, for example,
at least one of a crown ether, a crown ether, a podand, a lariat
ether, a calixarene, a calixcrown, or mixtures thereof. The
chelating agents can help improve the useful life of the lithium
ion battery by complexing with unwanted metal cations that may
become present in the battery's electrolyte solution while, at the
same time, not significantly interfering with the movement of
lithium ions between the negative and positive electrodes.
Inventors: |
Halalay; Ion C.; (Grosse
Pointe Park, MI) ; Harris; Stephen J.; (Bloomfield,
MI) ; Fuller; Timothy J.; (Pittsford, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM Global Technology Operations, LLC |
Detroit |
MI |
US |
|
|
Family ID: |
44151579 |
Appl. No.: |
14/336669 |
Filed: |
July 21, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12642313 |
Dec 18, 2009 |
8785054 |
|
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14336669 |
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Current U.S.
Class: |
429/215 ;
429/246; 525/348; 525/375; 525/379; 525/384 |
Current CPC
Class: |
H01M 2/162 20130101;
H01M 4/622 20130101; H01M 2220/30 20130101; H01M 2300/0025
20130101; H01M 10/0525 20130101; H01M 2/1653 20130101; Y10T
29/49108 20150115; Y02P 70/50 20151101; H01M 4/628 20130101; Y02E
60/10 20130101 |
Class at
Publication: |
429/215 ;
429/246; 525/384; 525/379; 525/375; 525/348 |
International
Class: |
H01M 4/62 20060101
H01M004/62; H01M 10/0525 20060101 H01M010/0525; H01M 2/16 20060101
H01M002/16 |
Claims
1. A lithium ion battery, comprising: a positive electrode; a
negative electrode; a microporous polymer separator soaked in an
electrolyte solution, the microporous polymer separator disposed
between the positive electrode and the negative electrode; and a
chelating agent chemically attached to the microporous polymer
separator, a binder material of the negative electrode, or a binder
material of the positive electrode, and wherein the one or more
chelating agents complex with transition metal cations but complex
less strongly with lithium ions so that the movement of lithium
ions between the negative and positive electrodes is not
substantially affected; wherein the chelating agent is selected
from the group consisting of a crown ether, a cryptand, a podand, a
lariat ether, a calixarene, a calixcrown, or a mixture of two or
more of these chelating agents.
2. The lithium ion battery as defined in claim 1 wherein the
microporous polymer separator, the binder material of the negative
electrode, or the binder material of the positive electrode is a
polymer and wherein the crown ether attached to the polymer is a
cyclic ether, and wherein oxygen atoms of the cyclic ether are to
complex with the transition metal cations.
3. The lithium ion battery as defined in claim 1 wherein the
chelating agent is selected from the group consisting of
15-crown-5, 15-crown-5 with at least one of its oxygen atoms
exchanged for a nitrogen atom, 18-crown-6, and 18-crown-6 with at
least one of its oxygen atoms exchanged for a nitrogen atom, and
wherein the chelating agent includes one of 2-hydroxymethyl,
hydroxymethyl-benzo, or 2-aminobenzo attached thereto.
4. The lithium ion battery as defined in claim 1 wherein the
chelating agent is the cryptand and includes one of
2-hydroxymethyl, hydroxymethyl-benzo, or 2-aminobenzo attached
thereto.
5. The lithium ion battery as defined in claim 1 wherein the
chelating agent is selected from the group consisting of:
##STR00006## ##STR00007## and wherein the chelating agent includes
one of 2-hydroxymethyl, hydroxymethyl-benzo, or 2-aminobenzo
attached thereto.
6. The lithium ion battery as defined in claim 1 wherein the
chelating agent attached to the microporous polymer separator, the
chelating agent attached to the binder material of the negative
electrode, or the chelating agent attached to the binder material
of the positive electrode is a crown ether substituted olefin that
is cross-linked with a cross-linking agent of divinylbenzene with
azobisisobutyronitrile.
7. The lithium ion battery as defined in claim 1 wherein the
microporous polymer separator is a polyolefin with a formula:
##STR00008## wherein n and x are integers, wherein X is I, Br, or
Cl, and wherein the chelating agent includes a group that
nucleophilically displaces X to attach the chelating agent to the
polyolefin, the group being selected from the group consisting of
2-hydroxymethyl, hydroxymethyl-benzo, or 2-aminobenzo.
8. The lithium ion battery as defined in claim 1 wherein a polymer
binder material of the negative electrode or a polymer binder
material of the positive electrode include at least one of
polyvinylidene fluoride, an ethylene polypropylene diene monomer
rubber, or carboxymethyl cellulose.
9. A method, comprising: forming a crown ether or a cryptand, the
crown ether or the cryptand having one of an OH group or an NH
group attached thereto; and replacing a halide ion attached to a
polymer with the crown ether or the cryptand, thereby forming a
polymer material having a pendant crown ether or a pendant
cryptand.
10. The method as defined in claim 9 wherein the OH group is
selected from the group consisting of 2-hydroxymethyl and
hydroxymethyl-benzo, or wherein the NH group is 2-aminobenzo.
11. The method as defined in claim 9 wherein the polymer is a
polyolefin with a formula: ##STR00009## wherein n and x are
integers, and wherein X is I, Br, or Cl.
12. The method as defined in claim 9 wherein the chelating agent is
selected from the group consisting of 15-crown-5, 15-crown-5 with
at least one of its oxygen atoms exchanged for a nitrogen atom,
18-crown-6, and 18-crown-6 with at least one of its oxygen atoms
exchanged for a nitrogen atom, and wherein the OH group is selected
from the group consisting of 2-hydroxymethyl and
hydroxymethyl-benzo, or the NH group is 2-aminobenzo.
13. The method as defined in claim 9 wherein the cryptand includes
one of 2-hydroxymethyl, hydroxymethyl-benzo, or 2-aminobenzo
attached thereto.
14. The method as defined in claim 9 wherein the crown ether is
selected from the group consisting of: ##STR00010## ##STR00011##
and wherein crown ether includes one of 2-hydroxymethyl,
hydroxymethyl-benzo, or 2-aminobenzo attached thereto.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/642,313, filed Dec. 18, 2009, which is
incorporated by reference herein in its entirety.
TECHNICAL FIELD
[0002] The technical field relates generally to secondary lithium
ion batteries and methods of making and using the same.
BACKGROUND
[0003] Secondary, or rechargeable, lithium ion batteries are well
known and often used in many stationary and portable devices such
as those encountered in the consumer electronic, automobile, and
aerospace industries. The lithium ion class of batteries have
gained popularity for various reasons including, but not limited
to, a relatively high energy density, a general nonappearance of
any memory effect when compared to other kinds of rechargeable
batteries, a relatively low internal resistance, and a low
self-discharge rate when not in use.
[0004] A lithium ion battery generally operates by reversibly
passing lithium ions between a negative electrode (sometimes called
the anode) and a positive electrode (sometimes called the cathode).
The negative and positive electrodes are situated on opposite sides
of a microporous polymer separator that is soaked with an
electrolyte solution suitable for conducting lithium ions. Each of
the negative and positive electrodes is also accommodated by a
current collector. The current collectors associated with the two
electrodes are connected by an interruptible external circuit that
allows an electric current to pass between the electrodes to
electrically balance the related migration of lithium ions. The
materials used to produce these various components of a lithium ion
battery are quite extensive. But in general, the negative electrode
typically includes a lithium intercalation host material, the
positive electrode typically includes a lithium-based active
material that can store lithium metal at a lower energy state than
the intercalation host material of the negative electrode, and the
electrolyte solution typically contains a lithium salt dissolved in
a non-aqueous solvent.
[0005] A lithium ion battery, or a plurality of lithium ion
batteries that are connected in series or in parallel, can be
utilized to reversibly supply power to an associated load device. A
brief discussion of a single power cycle beginning with battery
discharge can be insightful on this point.
[0006] To begin, during discharge, the negative electrode of a
lithium ion battery contains a high concentration of intercalated
lithium while the positive electrode is relatively depleted. The
establishment of a closed external circuit between the negative and
positive electrodes under such circumstances causes the extraction
of intercalated lithium from the negative anode. The extracted
lithium is then split into lithium ions and electrons. The lithium
ions are carried through the micropores of the interjacent polymer
separator from the negative electrode to the positive electrode by
the ionically conductive electrolyte solution while, at the same
time, the electrons are transmitted through the external circuit
from the negative electrode to the positive electrode (with the
help of the current collectors) to balance the overall
electrochemical cell. This flow of electrons through the external
circuit can be harnessed and fed to a load device until the level
of intercalated lithium in the negative electrode falls below a
workable level or the need for power ceases.
[0007] The lithium ion battery may be recharged after a partial or
full discharge of its available capacity. To charge or re-power the
lithium ion battery, an external power source is connected to the
positive and the negative electrodes to drive the reverse of
battery discharge electrochemical reactions. That is, during
charging, the external power source extracts the intercalated
lithium present in the positive electrode to produce lithium ions
and electrons. The lithium ions are carried back through the
separator by the electrolyte solution and the electrons are driven
back through the external circuit, both towards the negative
electrode. The lithium ions and electrons are ultimately reunited
at the negative electrode thus replenishing it with intercalated
lithium for future battery discharge.
[0008] The ability of lithium ion batteries to undergo such
repeated power cycling over their useful lifetimes makes them an
attractive and dependable power source. But lithium ion battery
technology is constantly in need of innovative developments and
contributions that can help advance to this and other related
fields of technological art.
SUMMARY
[0009] One exemplary embodiment of the invention is a microporous
polymer separator, for use in a lithium ion battery, to which one
or more chelating agents may be attached. The one or more chelating
agents can complex with metal cations but do not strongly complex
with lithium ions so that the movement of lithium ions across the
microporous polymer separator during operation of the lithium ion
battery is not substantially affected.
[0010] Another exemplary embodiment of the invention is a lithium
ion battery that may comprise a negative electrode, a positive
electrode, and a microporous polymer separator situated between the
negative electrode and the positive electrode. The negative
electrode may comprise a lithium host material and a polymer binder
material. The positive electrode may comprise a lithium-based
active material and a polymer binder material. One or more
chelating agents may be attached to at least one of the microporous
polymer separator, the binder material of the negative electrode,
or the binder material of the positive electrode. The one or more
chelating agents can complex with metal cations but do not strongly
complex with lithium ions so that the movement of lithium ions
between the negative and positive electrodes is not substantially
affected.
[0011] Yet another exemplary embodiment of the invention is a
lithium ion battery that may comprise a negative electrode, a
positive electrode, an interruptible external circuit that connects
the negative electrode and the positive electrode, a microporous
polymer separator to which one or more chelating agents are
attached situated between the negative electrode and the positive
electrode, and an electrolyte solution capable of conducting
lithium ions soaked into the negative electrode, the positive
electrode, and the microporous polymer separator. The microporous
polymer separator may comprise at least one of polyethylene or
polypropylene and have pendent groups or insoluble polymer bound
groups that comprise the chelating agents. The chelating agents can
complex with metal cations that leach from the positive electrode.
The chelating agents, moreover, may comprise at least one of a
crown ether, a podand, a lariat ether, a calixarene, a calixcrown,
or a mixture of two or more of these chelating agents.
[0012] Other exemplary embodiments of the invention will become
apparent from the detailed description provided hereinafter. It
should be understood that the detailed description and specific
examples, while disclosing exemplary embodiments of the invention,
are intended for purposes of illustration only and are not intended
to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Exemplary embodiments of the invention will become more
fully understood from the detailed description and the accompanying
drawings, wherein:
[0014] The FIGURE provided is a schematic and illustrative view of
a lithium ion battery, during discharge, according to various
embodiments of the invention. The separator is shown here to help
illustrate the flow of ions between the negative and positive
electrodes and, as such, is not necessarily drawn to scale.
DETAILED DESCRIPTION
[0015] The following description of the embodiment(s) is merely
exemplary in nature and is not intended to limit the invention, its
application, or uses.
[0016] A lithium ion battery can suffer cumulative capacity
reductions and other detrimental effects, such as the reduction of
solvent molecules, when destructive metal cations are introduced
into its various components. To help address such an issue, an
appropriate amount of one or more chelating agents may be attached
to the microporous polymer separator situated between the negative
and positive electrodes and/or to the polymer binder material used
to construct the negative electrode, the positive electrode, or
both. The chelating agents can be chosen to selectively complex
with unwanted metal cations that may become present in the
electrolyte solution over the life of the battery. For example, in
one embodiment, the immobilization of certain metal cations that
may dissolve into the electrolyte solution from the positive
electrode (i.e., cations of manganese, cobalt, and/or iron) can
help protect the lithium ion battery against negative electrode
poisoning and a resultant reduction to its capacity and useful
life. The chelating agents thus operate as metal cation scavenger
molecules that trap and immobilize unwanted metal cations so as to
prevent the migration of those metal cations through the
electrolyte solution. But at the same time the chelating agents do
not strongly complex with lithium ions and, as such, will not
adversely affect the movement of lithium ions between the negative
and positive electrodes to the point where an uncharacteristic
reduction of the expected electrical current to be supplied by the
battery occurs during discharge.
[0017] An exemplary and schematic illustration of a secondary
lithium ion battery 10 is shown that includes a negative electrode
12, a positive electrode 14, a microporous polymer separator 16
sandwiched between the two electrodes 12, 14, and an interruptible
external circuit 18 that connects the negative electrode 12 and the
positive electrode 14. Each of the negative electrode 12, the
positive electrode 14, and the microporous polymer separator 16 may
be soaked in an electrolyte solution capable of conducting lithium
ions. The microporous polymer separator 16, which operates as both
an electrical insulator and a mechanical support, is sandwiched
between the negative electrode 12 and the positive electrode 14 to
prevent physical contact between the two electrodes 12, 14 and the
occurrence of a short circuit. The microporous polymer separator
16, in addition to providing a physical barrier between the two
electrodes 12, 14, may also provide a minimal resistance to the
internal passage of lithium ions (and related anions) to help
ensure the lithium ion battery 10 functions properly. A
negative-side current collector 12a and a positive-side current
collector 14a may be positioned at or near the negative electrode
12 and the positive electrode 14, respectively, to collect and move
free electrons to and from the external circuit 18.
[0018] The lithium ion battery 10 may support a load device 22 that
can be operatively connected to the external circuit 18. The load
device 22 may be powered fully or partially by the electric current
passing through the external circuit 18 when the lithium ion
battery 10 is discharging. While the load device 22 may be any
number of known electrically-powered devices, a few specific
examples of a power-consuming load device include an electric motor
for a hybrid vehicle or an all-electrical vehicle, a laptop
computer, a cellular phone, and a cordless power tool, to name but
a few. The load device 22 may also, however, be a power-generating
apparatus that charges the lithium ion battery 10 for purposes of
storing energy. For instance, the tendency of windmills and solar
panel displays to variably and/or intermittently generate
electricity often results in a need to store surplus energy for
later use.
[0019] The lithium ion battery 10 can include a wide range of other
components that, while not depicted here, are nonetheless known to
skilled artisans. For instance, the lithium ion battery 10 may
include a casing, gaskets, terminal caps, and any other desirable
components or materials that may be situated between or around the
negative electrode 12, the positive electrode 12, and/or the
microporous polymer separator 16 for performance-related or other
practical purposes. Moreover, the size and shape of the lithium ion
battery 10 may vary depending on the particular application for
which it is designed. Battery-powered automobiles and hand-held
consumer electronic devices, for example, are two instances where
the lithium ion battery 10 would most likely be designed to
different size, capacity, and power-output specifications. The
lithium ion battery 10 may also be connected in series or parallel
with other similar lithium ion batteries to produce a greater
voltage output and power density if the load device 22 so
requires.
[0020] The lithium ion battery 10 can generate a useful electric
current during battery discharge by way of reversible
electrochemical reactions that occur when the external circuit 18
is closed to connect the negative electrode 12 and the positive
electrode 14 at a time when the negative electrode 12 contains a
sufficiently higher relative quantity of intercalated lithium. The
chemical potential difference between the positive electrode 14 and
the negative electrode 12--approximately 3.7 to 4.2 volts depending
on the exact chemical make-up of the electrodes 12, 14--drives
electrons produced by the oxidation of intercalated lithium at the
negative electrode 12 through the external circuit 18 towards the
positive electrode 14. Lithium ions, which are also produced at the
negative electrode, are concurrently carried by the electrolyte
solution through the microporous polymer separator 16 and towards
the positive electrode 14. The electrons flowing through the
external circuit 18 and the lithium ions migrating across the
microporous polymer separator 16 in the electrolyte solution
eventually reconcile and form intercalated lithium at the positive
electrode 14. The electric current passing through the external
circuit 18 can be harnessed and directed through the load device 22
until the intercalated lithium in the negative electrode 12 is
depleted and the capacity of the lithium ion battery 10 is
diminished.
[0021] The lithium ion battery 10 can be charged or re-powered at
any time by applying an external power source to the lithium ion
battery 10 to reverse the electrochemical reactions that occur
during battery discharge. The connection of an external power
source to the lithium ion battery 10 compels the otherwise
non-spontaneous oxidation of intercalated lithium at the positive
electrode 14 to produce electrons and lithium ions. The electrons,
which flow back towards the negative electrode 12 through the
external circuit 18, and the lithium ions, which are carried by the
electrolyte across the microporous polymer separator 16 back
towards the negative electrode 12, reunite at the negative
electrode 12 and replenish it with intercalated lithium for
consumption during the next battery discharge cycle. The external
power source that may be used to charge the lithium ion battery 10
may vary depending on the size, construction, and particular
end-use of the lithium ion battery 10. Some notable and exemplary
external power sources include, but are not limited to, an AC wall
outlet and a motor vehicle alternator.
[0022] The negative electrode 12 may include any lithium host
material that can sufficiently undergo lithium intercalation and
deintercalation while functioning as the negative terminal of the
lithium ion battery 10. The negative electrode 12 may also include
a polymer binder material to structurally hold the lithium host
material together. For example, in one embodiment, the negative
electrode 12 may be formed from graphite intermingled in at least
one of polyvinylidene fluoride (PVdF), an ethylene propylene diene
monomer (EPDM) rubber, or carboxymethyl cellulose (CMC). Graphite
is widely utilized to form the negative electrode because it
exhibits favorable lithium intercalation and deintercalation
characteristics, is relatively non-reactive, and can store lithium
in quantities that produce a relatively high energy density.
Commercial forms of graphite that may be used to fabricate the
negative electrode 12 are available from, for example, Timcal
Graphite & Carbon, headquartered in Bodio, Switzerland, Lonza
Group, headquartered in Basel, Switzerland, or Superior Graphite,
headquartered in Chicago, USA. Other materials can also be used to
form the negative electrode including, for example, lithium
titanate. The negative-side current collector 12a may be formed
from copper or any other appropriate electrically conductive
material known to skilled artisans.
[0023] The positive electrode 14 may be formed from any
lithium-based active material that can sufficiently undergo lithium
intercalation and deintercalation while functioning as the positive
terminal of the lithium ion battery 10. The positive electrode 14
may also include a polymer binder material to structurally hold the
lithium-based active material together. One common class of known
materials that can be used to form the positive electrode 14 is
layered lithium transitional metal oxides. For example, in various
embodiments, the positive electrode 14 may comprise at least one of
spinel lithium manganese oxide (LiMn.sub.2O.sub.4), lithium cobalt
oxide (LiCoO.sub.2), a nickel-manganese-cobalt oxide
[Li(Ni.sub.xMn.sub.yCo.sub.z)O.sub.2], or a lithium iron polyanion
oxide such as lithium iron phosphate (LiFePO.sub.4) or lithium iron
fluorophosphate (Li.sub.2FePO.sub.4F) intermingled in at least one
of polyvinylidene fluoride (PVdF), an ethylene propylene diene
monomer (EPDM) rubber, or carboxymethyl cellulose (CMC). Other
lithium-based active materials may also be utilized besides those
just mentioned. Those alternative materials include, but are not
limited to, lithium nickel oxide (LiNiO.sub.2), lithium aluminum
manganese oxide (Li.sub.xAl.sub.yMn.sub.1-yO.sub.2), and lithium
vanadium oxide (LiV.sub.2O.sub.5), to name but a few. The
positive-side current collector 14a may be formed from aluminum or
any other appropriate electrically conductive material known to
skilled artisans.
[0024] Any appropriate electrolyte solution that can conduct
lithium ions between the negative electrode 12 and the positive
electrode 14 may be used in the lithium ion battery 10. In one
embodiment, the electrolyte solution may be a non-aqueous liquid
electrolyte solution that includes a lithium salt dissolved in an
organic solvent or a mixture of organic solvents. Skilled artisans
are aware of the many non-aqueous liquid electrolyte solutions that
may be employed in the lithium ion battery 10 as well as how to
manufacture or commercially acquire them. A non-limiting list of
lithium salts that may be dissolved in an organic solvent to form
the non-aqueous liquid electrolyte solution include LiClO.sub.4,
LiAlCl.sub.4, LiI, LiBr, LiSCN, LiBF.sub.4,
LiB(C.sub.6H.sub.5).sub.4 LiAsF.sub.6, LiCF.sub.3SO.sub.3,
LiN(CF.sub.3SO.sub.2).sub.2, LiPF.sub.6, and mixtures thereof.
These and other similar lithium salts may be dissolved in a variety
of organic solvents such as, but not limited to, cyclic carbonates
(ethylene carbonate, propylene carbonate, butylene carbonate),
acyclic carbonates (dimethyl carbonate, diethyl carbonate,
ethylmethylcarbonate), aliphatic carboxylic esters (methyl formate,
methyl acetate, methyl propionate), .gamma.-lactones
(.gamma.-butyrolactone, .gamma.-valerolactone), chain structure
ethers (1,2-dimethoxyethane, 1-2-diethoxyethane,
ethoxymethoxyethane), cyclic ethers (tetrahydrofuran,
2-methyltetrahydrofuran), and mixtures thereof.
[0025] The microporous polymer separator 16 may comprise, in one
embodiment, a polyolefin. The polyolefin may be a homopolymer
(derived from a single monomer constituent) or a heteropolymer
(derived from more than one monomer constituent), either linear or
branched. If a heteropolymer derived from two monomer constituents
is employed, the polyolefin may assume any copolymer chain
arrangement including those of a block copolymer or a random
copolymer. The same holds true if the polyolefin is a heteropolymer
derived from more than two monomer constituents. In one embodiment,
the polyolefin may be polyethylene (PE), polypropylene (PP), or a
blend of PE and PP.
[0026] The microporous polymer separator 16 may be a single layer
or a multi-layer laminate fabricated from either a dry or wet
process. For example, in one embodiment, a single layer of the
polyolefin may constitute the entirety of the microporous polymer
separator 16. As another example, however, multiple discrete layers
of similar or dissimilar polyolefins may be assembled into the
microporous polymer separator 16. The microporous polymer separator
16 may also comprise other polymers in addition to the polyolefin
such as, but not limited to, polyethylene terephthalate (PET),
polyvinylidene fluoride (PVdF), and or a polyamide (Nylon). The
polyolefin layer, and any other optional polymer layers, may
further be included in the microporous polymer separator 16 as a
fibrous layer to help provide the microporous polymer separator 16
with appropriate structural and porosity characteristics. Skilled
artisans will undoubtedly know and understand the many available
polymers and commercial products from which the microporous polymer
separator 16 may be fabricated, as well as the many manufacturing
methods that may be employed to produce the microporous polymer
separator 16. A more complete discussion of single and multi-layer
lithium ion battery separators, and the dry and wet processes that
may be used to make them, can be found in P. Arora and Z. Zhang,
"Battery Separators," Chem. Rev., 104, 4424-4427 (2004).
[0027] The chelating agents, which may be attached to the
microporous polymer separator 16 and/or the polymer binders in at
least one of the negative electrode 12 or the positive electrodes
14, may be any of a variety of molecules that can complex with
unwanted metal cations to form stable and neutral compounds while,
at the same time, not adversely affecting the flow of lithium ions
between the negative and positive electrodes 12, 14. The particular
chelating agent or agents may, in some instances, be chosen to
selectively complex with certain metal cations that are known or
expected to be present in the electrolyte solution at some point
during operational lifetime of the lithium ion battery 10. For
example, spinel lithium manganese oxide (LiMn.sub.2O.sub.4) that
may be present in the positive electrode 14 may leach Mn.sup.2+
cations into the electrolyte solution during normal operation of
the lithium ion battery 10. These mobile Mn.sup.2+ cations, in
turn, can migrate through the electrolyte solution and across the
microporous polymer separator 16 until they eventually reach the
negative electrode 12. Moreover, if the negative electrode 12 is
formed from graphite, the Mn.sup.2+ cations that reach the negative
electrode 12 tend to undergo a reduction reaction and deposit on
the graphite surface since the standard redox potential of
Mn/Mn(II) is much higher than that of lithium intercalation into
graphite. The deposition of manganese onto graphite in the negative
electrode 12 catalyzes the reduction of solvent molecules at the
contaminated interface of the negative electrode 12 and the
electrolyte solution causing the evolution of gases. The poisoned
portion of the negative electrode 12 is essentially deactivated and
no longer able to facilitate the reversible gain and loss of
intercalated lithium. Similarly, the dissolution of cobalt cations
(Co.sup.2+) and iron cations (Fe.sup.2+) from lithium cobalt oxide
(LiCoO.sub.2) and lithium iron phosphate (LiFePO.sub.4),
respectively, that may be present in the positive electrode 14 can
also cause capacity losses in the lithium ion battery 10 by the
same or related mechanism. The leaching of Co.sup.2+ cations may
occur, in one instance, because of an ancillary chemical reaction
with various adhesives normally used in the packaging of the
lithium ion battery 10. The leaching of Fe.sup.2+ cations may
occur, in one instance, because of the presence of hydrofluoric
acid that may be produced through the ingress and egress of water
into the electrolyte solution.
[0028] But regardless of the lithium-based active material(s) used
in the positive electrode 14, the leaching rate of metal cations
into the electrolyte solution may vary. The leaching rate of metal
cations from positive electrode 14 may be relatively slow and
require several years for the electrolyte solution to accumulate a
concentration of associated metal cations measurable in parts per
million (ppm). The leaching rate of metal cations from the positive
electrode 14 may also, on the other hand, be relatively fast in
that the concentration of associated metal cations in the
electrolyte solution increases by about 0.1 weight percent per
battery power cycle. The leaching of any amount of metal cations
from the positive electrode 14, whether slow or fast, can
nevertheless poison large areas of the graphite in the negative
electrode 12 and ultimately cause a noticeable and
performance-affecting reduction in capacity of the lithium ion
battery 10. An amount of chelating agents effective to sequester
the cumulative dissolution of metal cations into the electrolyte
solution during the operational lifetime of the lithium ion battery
10 may therefore be attached to the microporous polymer separator
16 and/or the polymer binding materials in at least one of the
negative or positive electrodes 12, 14. The exact amount of
chelating agents employed, which may vary considerably, is
generally predicated on the chemistry of the lithium ion battery
10, the compositional make-up of the negative and positive
electrodes 12, 14, and the expected or observed rate at which
unwanted metal cations are introduced into the electrolyte solution
during operation of the lithium ion battery.
[0029] The chelating agents may comprise, for example, at least one
of a crown ether, a podand, a lariat ether, a calixarene, a
calixcrown, or mixtures thereof. These chelating agents are useful
because they will not strongly complex with the relatively small
lithium ions moving between the negative and positive electrodes
12, 14 because of their size and spatial constructions. Skilled
artisans will generally know and understand, or be able identify,
the many molecular compounds that may constitute these classes of
chelating agents. A generalized description of these chelating
agents is nonetheless provided here for convenience.
[0030] A crown ether is a macrocyclic polyether in which the
polyether ring includes oxygen donor atoms that can complex with a
metal cation. Some or all of the oxygen donor atoms in the
polyether ring may be exchanged for nitrogen atoms, a class of
crown ethers known as azacrowns, or sulfur atoms, a class of crown
ethers known as thiacrowns. The crown ether may be monocyclic, in
which the crown ether forms a somewhat two-dimensional ring for
complexing with a metal cation, or polycyclic, in which the crown
ether forms a more three-dimensional cage for complexing with a
metal cation. One example of a polycyclic crown ether is a
cryptand. The crown ether may also be substituted at any location
along its polyether ring by any of a variety of groups known to
those skilled in the art. A podand is an acyclic polyether ligand
that includes donor-group-bearing arms that can complex with a
metal cation. A lariat ether is a crown ether that includes a
donor-group-bearing side-arm that provides additional metal cation
binding sites beyond those present on the polyether ring. A
calixarene is a metacyclophane of methylene-bridged phenol units,
and is generally found in one of a cone, partial cone,
1,2-alternate, or 1,3-alternate conformation. A calixcrown is a
calixarene that includes a polyether ring that links two phenolic
oxygens of the calixarene framework. The indifference these
chelating agents show towards complexing with lithium ions is
likely ascribed to their relatively large polyether ring or cage
structures and/or the spatial orientation of their functional
donor-group-bearing arms when compared to the relatively small size
of lithium ions. Analogs and structurally related molecules of the
chelating agents just mentioned may also be employed.
[0031] A nonexhaustive and exemplary list of crown ethers that can
complex with metal cations which may, for example, leach into the
electrolyte solution from the positive electrode 14 (such as
cations of manganese, cobalt, and iron) includes (1) 15-crown-5,
(2) dibenzo-15-crown-5, (3) 18-crown-6, (4) benzo-18-crown-6, (5)
dibenzo-18-crown-6, (6) dibenzo-21-crown-7, (7)
dicyclohexano-18-crown-6, (8) dicyclohexano-24-crown-8, (9)
poly(dibenzo-18-crown-6), (10) 1,4,7,10,13,16-hexathia-18-crown-6,
(11) 1,4,7,10,13,16-hexaaza-18-crown-6, (12) 1-aza-18-crown-6, (13)
1,10-diaza-18-crown-6, (14) N,N'-dibenzyl-4,13-diaza-18-crown-6,
and (15)
4,7,13,16,21,24-hexaoxa-1,10-diazabycyclo[9.8.8]hexacosane, the
structures of which are shown below. The hydrogen atoms in
structures 11-13 are assumed.
##STR00001## ##STR00002## ##STR00003##
[0032] Some more examples of crown ethers, including thiacrowns and
azacrowns, that may be attached to the microporous polymer
separator 16 can be found in W. Walkowiak and C. A. Kozlowski,
"Macrocycle Carriers for Separation of Metal Ions in Liquid
Membrane Processes--A Review," Desalination 240, Table 1 on pg. 189
(compounds 1-15 that are not already mentioned above) (2009); R. L
Bruening, R. M. Izatt, and J. S. Bradshaw, "Understanding
Cation-Macrocycle Binding Selectivity in Single-Solvent
Extractions, and Liquid Membrane Systems by Quantifying
Thermodynamic Interactions, FIG. 1 on pg. 112 in "Cation Binding by
Macrocycles," Y. Inoue and G. W. Gokel (editors), Chapter 2, 1990,
Marcel Dekker Inc., New York and Basel; J. L. Tonor, "Modern
Aspects of Host-Guest Chemistry: Molecular Modeling and
Conformationally Restricted Hosts," FIG. 2 on pg. 82 in "Crown
Ethers and Analogs," S. Patai and Z. Rappaport (editors), Chapter
3, 1989, John Wiley and Sons, New York; F. Vogtle and E. Weber,
"Crown-ether-complexes and Selectivity," FIGS. 1, 2, and 3 on pg.
209, 210, and 211, respectively, in "Crown Ethers and Analogs," S.
Patai and Z. Rappaport (editors), Chapter 4, 1989, John Wiley and
Sons, New York, the above-identified portions of each reference
being hereby incorporated by reference.
[0033] A nonexhaustive and exemplary list of podands that can
complex with metal cations which may, for example, leach into the
electrolyte solution from the positive electrode 14 can be found in
W. Walkowiak and C. A. Kozlowski, "Macrocycle Carriers for
Separation of Metal Ions in Liquid Membrane Processes--A Review,"
Desalination 240, Table 2 on pg. 190 (compounds 32a and 32b)
(2009); A. Shahrisa and A. Banaei, "Chemistry of Pyrones, Part 3:
New Podands of 4H-Pyran-4-ones, 5 Molecules," FIGS. 1 and 3 on pg.
201 (2000); and F. Vogtle and E. Weber, "Crown-ether-complexes and
Selectivity," FIGS. 4, 5, 6, and 7 on pg. 212, 213, 214, and 215,
respectively, in "Crown Ethers and Analogs," S. Patai and Z.
Rappaport (editors), Chapter 4, 1989, John Wiley and Sons, New
York; and Crown Ethers and Analogs, edited by Patai and Rappoport,
(1989), the above-identified portions of each reference being
hereby incorporated by reference.
[0034] A nonexhaustive and exemplary list of lariat ethers that can
complex with metal cations which may, for example, leach into the
electrolyte solution from the positive electrode 14 can be found in
W. Walkowiak and C. A. Kozlowski, "Macrocycle Carriers for
Separation of Metal Ions in Liquid Membrane Processes--A Review,"
Desalination 240, Table 1 on pg. 189 (compounds 16-18) (2009); and
E. Weber, "New Developments in Crown Ether Chemistry: Lariats,
Spherands, and Second-Sphere Complexes," FIGS. 2, 4, and 6 on pg.
307, 309, and 315, respectively, in "Crown Ethers and Analogs," S.
Patai and Z. Rappaport (editors), Chapter 5, 1989, John Wiley and
Sons, New York, the above-identified portions of each reference
being hereby incorporated by reference.
[0035] A nonexhaustive and exemplary list of calixarenes that can
complex with metal cations which may, for example, leach into the
electrolyte solution from the positive electrode 14 can be found in
W. Walkowiak and C. A. Kozlowski, "Macrocycle Carriers for
Separation of Metal Ions in Liquid Membrane Processes--A Review,"
Desalination 240, Table 2 on pg. 190 (compounds 22-23) (2009); and
J. L. Atwood, "Cation Complexation by Calixarenes," FIGS. 6 and 7
on pg. 587 (the ester functionalized calixarenes) in "Cation
Binding by Macrocycles," Y. Inoue and G. W. Gokel (editors),
Chapter 15, 1990, Marcel Dekker Inc., New York and Basel, the
above-identified portions of each reference being hereby
incorporated by reference.
[0036] A nonexhaustive and exemplary list of calixcrowns that can
complex with metal cations which may, for example, leach into the
electrolyte solution from the positive electrode 14 can be found in
W. Walkowiak and C. A. Kozlowski, "Macrocycle Carriers for
Separation of Metal Ions in Liquid Membrane Processes--A Review,"
Desalination 240, Table 2 on pg. 190 (compounds 24-27, compound 28
with ester functionality, and compounds 30-31) (2009), the
above-identified portions of each reference being hereby
incorporated by reference.
[0037] There are, of course, many other crown ethers, podands,
lariat ethers, calixarenes, calixcrowns, and related chelating
agents that are known to skilled artisans, but are not specifically
mentioned here, that can be attached to the microporous polymer
separator 16 to sequester and immobilize unwanted metal cations
that may be introduced into the electrolyte solution of the lithium
ion battery 10.
[0038] The chelating agents may be attached to the microporous
polymer separator 16 and the polymer binders of the negative and
positive electrodes 12, 14 by any known method. For example, in one
embodiment, a pendant group that comprises the chelating agent may
be grafted onto the polyolefin used to make the microporous polymer
separator 16. The chelating agents may be attached uniformly
throughout polyolefin or they may be locally attached at
predetermined locations. A greater concentration of the chelating
agents may, for example, be provided on the side of the microporous
polymer separator 16 that faces the positive electrode 14. Such a
build-up of chelating agents on the positive-electrode-side of the
microporous polymer separator 16 can help facilitate the earliest
possible sequestering of any destructive metal cations that leach
into the electrolyte solution from the positive electrode 14.
Pendent groups that comprise the chelating agents may also be
similarly grafted onto the other polymers in the microporous
polymer separator 16, if present. In another embodiment, an
insoluble polymer bound group that comprises the chelating agent
may be entangled in, and optionally crosslinked to, the polymer
matrix of the microporous polymer separator 16 and/or the polymer
binder materials of at least one of the negative or positive
electrodes 12, 14. The polymer bound group may be polyolefin, or
some other polymer with similar properties, that includes a pendent
group that comprises the chelating agent.
[0039] A poly(1-olefin) may be prepared, for instance, from the
Ziegler-Natta polymerization of functionally substituted
polyolefins or by metathesis polymerization. The resultant
poly(1-olefins) may then be functionalized with the chelating
agents. The same chelating agent substituted polyolefins may also
be prepared by the polymerization of .alpha.,.omega.-olefins or
pre-formed prepolymers that have been substituted with pendant
chelating agent groups. Polyolefin heteropolymers, such as
polyundecylenol, may be formed by either method and generally
involve the controlled feed of similarly sized (i.e., number of
carbons) olefin monomers or prepolymers during polymerization. The
chelating agent substituted polyolefins, once prepared, may then be
incorporated into the microporous polymer separator 16. In one
embodiment, the chelating agent substituted polyolefins may be
manufactured into a fairly rigid fibrous polyolefin layer that may
constitute all or part of the microporous polymer separator 16. In
another embodiment, however, the chelating agent substituted
polyolefins may be insolubly bound within the polymer matrix of a
separate fibrous polymer layer that is intended for use as all or
part of the microporous polymer separator 16, or they may be
insolubly bound within the polymer matrix of a polymer binder
materials that is intended to be included in at least one of the
negative or positive electrodes 12, 14.
[0040] The following examples are provided to help illustrate how a
chelating agent substituted polyolefin may be prepared, and how
such polyolefins may be incorporated into the microporous polymer
separator 16 and/or the polymer binder materials of at least one of
the negative or positive electrodes 12, 14. Example 1 demonstrates
the preparation of a polyolefin that includes pendent crown ether
groups in which a functionally substituted polyolefin was
polymerized and then substituted with crown ether groups. Example 2
demonstrates the preparation of a polyolefin that includes pendent
crown ether groups in which olefins were substituted with crown
ether groups and then polymerized. Example 3 demonstrates the
manufacture of a microporous polymer separator from the polyolefins
of either Example 1 or Example 2. The microporous polymer separator
manufactured in Example 3 includes a polyolefin layer having
pendent crown ether groups. Example 4 demonstrates the manufacture
of a microporous polymer separator or a negative electrode. In that
Example, crown ether substituted polyolefins are insolubly bound
within the polymer matrix of a commercially available polyolefin
battery separator or a commercially available polymer binder
material. Those materials may then be incorporated into a
microporous polymer separator or a negative electrode,
respectively.
EXAMPLE 1
[0041] In this example, a polyolefin with pendent 18-crown-6 groups
(crown ether chelating agent) is prepared by the Zeigler-Natta
polymerization of a halogenated polyolefin that is subsequently
substituted with functionalized crown ether groups. The halogenated
polyolefins may be formed by the direct polymerization of
halo-functionalized monomers or the chemical modification of
pre-formed prepolymers. To accomplish this, at least one
.alpha.,.omega.-olefin such as 11-undecylenyl bromide (or iodide),
6-bromo-1-hexene, or 5-bromo-1-pentene may be polymerized with at
least one 1-olefin such as ethane, propene, or 1-butene at a
prefixed .alpha.,.omega.-olefin:1-olefin weight ratio of, for
example, 1:9, 2:8, 3:7, or 5:5 in toluene. A catalyst, such as
TiCl.sub.3.AA/Et.sub.2AlCl, may be used to make isotactic
poly-.alpha.-olefins that form .alpha.-helix structures and
polymerize the .omega.-substituted .alpha.-olefins. This
polymerization reaction proceeds most efficiently when bulky
monomer or prepolymer functionalized units that do not coordinate
with the catalyst are used [e.g.
CH.sub.2.dbd.CH--(CH.sub.2).sub.y--X]. Large halo groups (X) may
also enhance the polymerization reaction (i.e., I>Br>Cl). The
resultant polymers, which are soluble in hot toluene, can form
carboxylic acid and alcohol functional groups by protection with,
for example, trimethylsilyl-groups [--Si(CH.sub.3).sub.3], which
are readily removed on work-up with aqueous acids. Nucleophilic
displacement of the halide ion with 2-hydroxymethyl-18-crown-6,
hydroxymethyl-benzo-18-crown-6, or 2-aminobenzo-18-crown-6 in the
presence of potassium carbonate and/or lutidine may then be
achieved to attach pendent groups containing 18-crown-6 to the
polyolefins. Moreover, at high concentrations of crown ether
substituent groups, the polyolefins become less crystalline and may
therefore be reinforced with 1,6-hexadience as a co-reactant to
cross-link the polyolefins. The overall reaction in which pendent
18-crown-6 groups are grafted onto a polyolefin is shown below,
where X may be I or Br, and Y may be 2-hydroxymethyl,
hydroxymethyl-benzo, or 2-aminobenzo.
##STR00004##
EXAMPLE 2
[0042] In this example, a polyolefin with pendent 18-crown-6 groups
(crown ether chelating agent) is prepared by polymerizing
.alpha.,.omega.-olefins or pre-formed prepolymers that have first
been substituted with pendant crown ether groups. Crown ether
substituted .alpha.,.omega.-olefins may be prepared by reacting at
least one of 11-undecylenyl bromide (or iodide), 6-bromo-1-hexene,
or 5-bromo-1-pentene with at least one of hydroxymethyl-18-crown-6
or hydroxymethyl-benzo-18-crown-6 in N,N-dimethylacetamide. Alcohol
functional groups may be formed on the .alpha.,.omega.-olefins by
protection with, for example, trimethylsilyl-groups
[--Si(CH.sub.3).sub.3], which are readily removed on work-up with
aqueous acids. Nucleophilic displacement of the halide ion with
2-hydroxymethyl-18-crown-6 or hydroxymethyl-benzo-18-crown-6 in the
presence of potassium carbonate and/or lutidine may then proceed
until the bromo (or iodo) groups on the .alpha.,.omega.-olefins are
replaced with 18-crown-6 groups. The crown ether substituted
a,w-olefins are then polymerized with at least one 1-olefin such as
ethane, propene, or 1-butene at a pre-fixed
.alpha.,.omega.-olefin:1-olefin weight ratio of, for example, 1:9,
2:8, 3:7, or 5:5 in toluene. A catalyst, such as
TiCl.sub.3.AA/Et.sub.2AlCl, may be used to make isotactic
poly-.alpha.-olefins that form .alpha.-helix structures and
polymerize the .omega.-substituted .alpha.-olefins. Moreover, at
high concentrations of crown ether substituent groups, the
polyolefins become less crystalline and may therefore be reinforced
with 1,6-hexadience as a co-reactant to cross-link the polyolefin.
The overall reaction in which pendent 18-crown-6 groups are grafted
onto a polyolefin is shown below, where X may be I or Br, and Y may
be 2-hydroxymethyl, hydroxymethyl-benzo, or 2-aminobenzo.
##STR00005##
[0043] In a typical reaction, 6-bromo-1-hexene is allowed to react
with a one molar ratio of hydroxymethyl-benzo-18-crown-6 in
N,N-dimethylacetamide for 1 week at 50.degree. C. under argon in a
sealed vessel in the presence of excess potassium carbonate and a
molecular equivalent of lutidine. The reaction mixture is filtered
and the solvent and lutidine are then removed under vacuum and
1-hexyl-6-benzo-18-crown-6 is purified on silica gel by column
chromatography eluting with tetrahydrofuran, methylene chloride, or
ethyl acetate and hexanes. After removal of the solvent, the
residue is dissolved in 10 wt. % toluene, 1 wt. % 1,6-hexadiene,
and with 89 wt. % 1-butene bubbled into a glass beverage bottle
with a rubber septum that is situated in an ice bath. The reactants
in toluene are double-needle, dropwise transferred into another
beverage bottle with a rubber septum under argon, situated in an
ice bath, and containing a magnetic stir bar, toluene,
TiCl.sub.3.AA, 25 wt. % diethylaluminum chloride in toluene, and
optionally a 1.1 molar solution of diethyl zinc, all of which are
added to methanol using a Waring blender to fibrillate the
precipitated crown ether substituted polyolefin as a fibrous
pulp.
OTHER EXAMPLES
[0044] A more complete discussion of various techniques that can be
used to graft crown ethers onto polymer backbones can be found in
J. Smid, Pure Appl. Chem., 48, 343 (1976), J. Smid, Makrom. Chem.
Supp., 5, 203 (1981), J. Smid, Pure Appi. Chem., 54, 2129 (1982),
and U. Tunca and Y. Yagci, "Crown Ether Containing Polymers," Prog.
Polym. Sci., 19, 233-286 (1994). Another method of making
poly(olefins) with pendent crown ethers is to prepare poly(vinyl
benzyl alcohol) containing polymers, as discussed in U.S. Pat. No.
6,200,716 to Fuller, and then react those polymers with
chloromethyl-benzo-18-crown-6 in N,N-dimethylacetamide. Still
another method involves preparing olefinic polymers with
undecylenyl alcohol groups and allowing those polymers to react
with lithium hydride in tetrahydrofuran in the presence of
chloromethyl-benzo-18-crown-6.
EXAMPLE 3
[0045] The crown ether substituted polyolefins prepared by the
method of either Example 1 or Example 2 may be added to a
non-solvent such as methanol to form insoluble flocculated fibrous
materials (flocs). The crown ether substituted polyolefins may,
alternatively, be quenched with methanol, washed with water, and
then stripped of toluene under reduced pressure. The polyolefins
may then be fibrillated in a non-solvent such as water using a
Waring blender. Next, the fibrillated polyolefins may be poured
onto and laid down on a porous screen. The wet pulp polyolefin
material may then be pressed to remove any residual non-solvent to
form a fibrous mat, and subsequently hot pressed below the melting
point of the polyolefin to form a fairly rigid crown ether
substituted fibrous polyolefin material layer. The resultant
polymer layer may then be utilized in a lithium ion battery as
either a single layer microporous polymer separator or as part of a
multi-layer microporous polymer separator.
EXAMPLE 4
[0046] The crown ether substituted olefins (vinyl benzo-18-crown-6)
prepared by the method described by J. Smid (see OTHER EXAMPLES
above), or purchased from Aldrich of Milwaukee, Wis., may be
dissolved in a toluene or benzene solution that optionally, but
preferably, includes a cross-linking agent such as divinylbenzene
with azobisisobutyronitrile (0.1 wt. % monomer mass). A commercial
polyolefin lithium ion battery separator or a commercially
available binder material may be dipped into the solution with
subsequent heating under nitrogen between 60.degree. C. and
80.degree. C. so that polymerization of the crown ether substituted
olefins can occur in the presence of the separator or polymer
binder material. Commercial polyolefin battery separators, either
single or multi-layered, are available from Asahi Kasei,
headquartered in Tokyo, Japan, Celgard LLC, headquartered in
Charlotte, N.C., Ube Industries, headquartered in Tokyo, Japan, and
Mitsui Chemicals, headquartered in Tokyo, Japan, to name but a few
manufacturers. The dissolved crown ether substituted polyolefins,
at this point, become snagged in the polymer matrix of the
commercial battery separator or the commercially available polymer
binder material. Later, when the commercial battery separator or
the commercially available polymer binder material is removed from
the solution and air dried, the entrapped crown ether substituted
polyolefins become insoluble polymer bound polyolefin particles.
The presence of a cross-linker can enhance the entanglement of the
crown ether substituted polyolefins contained in the commercial
battery separator or the commercially available polymer binder
material by promoting the formation of stronger polymer-polymer
bonds between the polymer bound crown ether substituted polyolefins
and between the polymer bound crown ether substituted polyolefins
and the commercial battery separator/commercial polymer binder
materials.
[0047] The above description of embodiments is merely exemplary in
nature and, thus, variations thereof are not to be regarded as a
departure from the spirit and scope of the invention.
* * * * *